This invention relates to a method and apparatus for stitching print swaths in an image-rendering device such as an acoustic ink printer. More particularly, the invention is directed to a method implemented in an apparatus to reduce the visual artifact caused by inaccurate paper advance between neighboring swaths of an ink emitter printhead and drop misdirection. The method includes the provision of a xe2x80x9cpuzzle cutxe2x80x9d or xe2x80x9czipperxe2x80x9d edge between swaths. In this regard, the image is divided into swaths and the edges thereof are dithered to vary the depth of the cut in accordance with the expected paper advance accuracy and other printing characteristics such as noise and variations in the width of print swaths for different printheads.
While the invention is particularly directed to the art of reducing artifacts in acoustic ink printing applications, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention may be used in ink jet printing or other types of printing where an array of ink emitters or ejectors is used to print swaths across a page on a pixel basis.
By way of background, it is advantageous to understand the basic operation of acoustic ink printing emitters to fully appreciate the problems addressed by and advantages of the present invention. In this regard, FIG. 1 provides a view of an exemplary acoustic ink printing ejector 10. While a single ejector is illustrated, an acoustic ink printhead typically consists of a number of the ejectors arranged in an array configuration. A typical acoustic ink printhead includes, for example, 1024 emitters that emit drops on a print medium. Drops of ink are emitted to form pixels of the image. A pixel can comprise no drops, one drop or multiple drops. In addition, multiple printheads are generally used in a printer. Moreover, it is to be appreciated that material other than ink may be emitted by the printhead.
As shown, ejector 10 includes a glass layer 12 having an electrode 14 disposed thereon. A piezoelectric layer 16, preferably formed of zinc oxide, is positioned on the electrode layer 14 and an electrode 18 is disposed on the piezoelectric layer 16. Electrode layer 14 and electrode 18 are connected through a surface wiring pattern representatively shown by lines 20 and 22 to a radio frequency (RF) power source 24 which generates power that is transferred to the electrodes 14 and 18. On a side opposite the electrode layer 14, a lens 26, such as a concentric Fresnel lens, or other appropriate lens, is formed. Spaced from the lens 26 is a liquid level control plate (also called an orifice plate) 28, having an opening or orifice 30 formed therein. Fluid, or ink, 32 is retained between the orifice plate 28 and the glass layer 12. The orifice 30 is aligned with the lens 26 to facilitate emission of a droplet 34 from ink surface, or meniscus, 36. Ink surface 36 is, of course, exposed by the orifice 30.
The lens 26, the electrode layer 14, the piezoelectric layer 16 and the electrode 28 are formed on the glass layer 12 through photolithographic techniques. The orifice plate 28 is subsequently positioned to be spaced from the glass layer 12. The ink 32 is fed into the space between the orifice plate 28 and the glass layer 12 from an ink supply.
As noted above, an acoustic ink printing application, acoustic ink emitters of FIG. 1 are arranged in an array on each printhead. It should be recognized that, in most cases, the printheads used are not full page width array printheads so printing must be accomplished in print swaths across each page. As a result, visual artifacts may appear between the swathes. That is, if a swath overlaps with another swath, dark artifacts appear in the image. On the other hand, if the swaths are not placed close enough together to allow the printed ink to spread and create a substantially uniform layer at the swath boundary, the color of the underlying print medium may show through. For a white printing medium, this would appear as a white line between the swaths.
U.S. Pat. No. 5, 053,793 to White et al., and commonly assigned, relates to electrostatic recorders in which writing is accomplished by contemporaneously pulsing the voltage of sets of recording stylus electrodes, arranged in an array, of selected complementary electrodes. More particularly, the invention relates to laterally shifting, or dithering, the boundaries of the sets of stylus electrodes and subsequent scan lines so as to prevent the set boundaries from being aligned, in order to eliminate visible striations extending in the process direction.
However, it would nonetheless be desirable to have a system and/or method to address the problems noted above in the acoustic ink printing environment, or similar such environments utilizing bit maps, emitters, and swath-type printing.
As such, the present invention contemplates a new and improved method and apparatus for stitching print swaths in an image-rendering device that resolve the above-referenced difficulties and others.
A method and apparatus for stitching print swaths in an image-rendering device are provided.
In one aspect of the invention, a method comprises steps of obtaining an image comprising pixels arranged in columns and rows and creating stitch regions in the image, the stitch regions 1) being defined by a predetermined number of columns or pixels, 2) corresponding to overlap regions of the print swaths and 3) including a transition from the first print swath to the second print swath in the overlap region, the transition occurring at different pixel locations for selected rows of pixels of the image.
In another aspect of the invention, a method comprises the steps of obtaining an image, generating a bitmap based in the image, selecting swath portions of the image based on the bitmap, dithering edges of the swath portions, storing print data on the swath portions having the dithered edges, and printing the image based on the print data.
In another aspect of the invention, an apparatus comprises a bitmap generator operative to generate a bitmap based on an input image, an image processor including a swath portion determining module operative to determine swath portions of the image based on the bitmap and a dithering module operative to dither edges of the swath portions, and a print control module operative to control printheads based on the swath portions having dithered edges.
Further scope of the applicability of the present invention will become apparent from the detailed description provided below. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.